Friday, 1/30: The Electromagnetic Spectrum

We quickly talked about the EM spectrum today, then used the rest of the period to start the homework. Below you will find the notes and homework assignment, including a sample homework. Do not turn in my homework; make your own, please.

Thursday, 1/29: Finding the Speed of Light

Over the centuries, many methods have been used to find, or attempt to find, the speed of light. Today we used a very simple method.

We start with an equation we've seen before for the speed of a wave: speed = wavelength x frequency

The frequency can be found written on the back of the microwave. Ours was f=2.4GHz or 2,400,000,000 Hz.

Next, we microwaved some candy bars for about 15 seconds (without the turntable). This produced melty spots that were half a wavelength apart (see notes). By measuring this, we were able to find the wavelength of the microwaves.

Your homework is to calculate the speed of light using f= 2,400,000,000 Hz and the wavelengths we found in class. Here are some sample wavelengths to use if you weren't in class:

0.12 m, 0.13m, and 0.15 m.

Those students that brought candy bars got to make s'mores with the leftovers. S'mores! Yay!

Notes:


Edit: Here is a good explanation of a similar experiment.

Wednesday, 1/28: Test 1: Waves and Sound

Today there is (necessarily short) test covering waves and sound. You are allowed a 3"x5" card of notes.

Tuesday, 1/27: Shadows and Eclipses

We all know what a shadow is, don't we? Or do we? Notes below. No homework tonight, but you do have a test about waves and sound tomorrow.

Monday, 1/26: Introduction to Light

Today we spoke briefly about what various people of the past thought about light and how we see things. But for the rest of the time each period discussed whatever they wanted to; third period was my favorite, where we talked about time travel and three of its consequences according to various scifi stories. Awesome.

Friday, 1/23: Test 1 Review Problems

We will have a short test next Wednesday, January 28. It will cover waves and sound. Today you had time to work on some review problems: p.388 #7, 8, 10, 31, 33 and p. 401 #1, 5, 10, 20, 24. Please complete these in your notebook. Since you cannot take the book home, the problems also appear below.

p.388

7.) Distinguish between the period and the frequency of a vibration or a wave. How do they relate to one another?

8.) Does the medium in which a wave travels move along with the wave itself? Defend your answer.

10.) As the frequency of sound is increased, does the wavelength increase of decrease? Give an example.

31.) Astronomers find that light coming from point A at the edge of the sun has a slightly higher frequency than light from point B at the opposite side. What do these measurements tell you about the sun's motion?

33.) Whenever you watch a high-flying aircraft overhead, it seems that its sound comes from behind the craft rather than from where you see it. Why is this?

p.401

1.) What is the source of all sounds?

5.) a. Distinguish between compressions and rarefactions of a sound wave.
b. How are compressions and rarefactions produced?

10.) Why is sound louder when a vibration source is held to a sounding board?

20.) What is the beat frequency when when a 494-Hz tuning fork and a 496-Hz tuning fork are sounded together?

24.) What two physics mistakes occur in a science fiction movie when you see and hear at the same time a distant explosion in outer space?

Thursday, 1/22: Earthquakes and Tsunamis

These are two kinds of waves that are cool to discuss. And guess what: they act just like the other waves we've been studying!

Remember, Concept-Development 26-1 is due today.

Wednesday, 1/21: Lightning and Thunder

Today I decided to show you the sort of math I have not been making you do. Be grateful, young sirs and madames. So below you will find the derivation of the equation for finding the distance to lightning (or an earthquake) using the speed of the two waves and the time between their arrivals.

Homework: Concept-Development 26-1. This is due tomorrow.

Tuesday, 1/20: Standing Waves Lab

The lab we completed today may be found here: http://docs.google.com/Doc?id=dccgmhcd_41f59mg6d3 .
Sorry the diagram is not labelled; the text boxes did not publish correctly. The dots are nodes and the dotted vertical lines are antinodes.

This is due tomorrow.

Friday, 1/16: Doppler Effect

Today we demonstrated and explained the Doppler Effect. Remember, this applies to any wave, not just sound waves.

Thursday, 1/15: Teacher out Sick

I was out today but should be back tomorrow. The substitute assignment was to read "Ten Things You Don't Know About the Earth," by the totally awesome Phil Plait. I recommend any of his Bad Astronomy blog entries.

Because I wasn't there to collect it today, the ranking task homework assigned yesterday is now due tomorrow.

Wednesday, 1/14: Forced Vibration and Resonance

Today we talked about forced vibration, natural frequency, and resonance. The partial notes are below. A ranking task worksheet about speed of waves and superposition was assigned as homework and is due tomorrow.

Edit: The teacher was out sick on Thursday, so the homework is due Friday, 1/16.

Tuesday, 1/13: Sound and Beats

Today we used a tone generator to find the frequency range humans can hear and to listen to beats. The notes are below. Concept Development 25-3 is due today.

Monday, 1/12: Vibrations and Sound

Today we saw a demonstration and discussed what exactly causes sound waves. Homework tonight: on your own paper, answer the question, "Can you hear sound in outer space? Why or why not?"
Due today: Concept Development 25-1.

Friday, 1/9: Wave Interference

Bellwork and notes are below. Concept-Development 25-3 was assigned today and will be due next Tuesday, 1/13.

Thursday, 1/8: Waves!

Waves, waves, waves! Notes are below, followed by bellwork. Concept Development 25-1 was assigned today and will be due next Monday, 1/12.


Bellwork:

Wednesday, 1/7: Wave Lab I Review

Today we went over what groups saw in lab and how that relates to what we'll be doing for the next couple of weeks.

Monday, 1/5 and Tuesday, 1/6: Wave Lab I

Welcome back! The first two days of school we are playing with the properties of mechanical waves using giant Slinkies and springs. On Wednesday we will go over the properties you will have observed during lab.